1. Field of the Invention
The present invention relates to a technology for converting color data into two-color data having black and other color.
2. Description of the Related Art
Recently, a document often includes characters written in color, for example, to highlight a specific area of the document. One of methods of printing such a document is a two-color print method by which colors of characters included in a document are converted into two colors of black and a different color, for example, red. The two-color print method includes two types of print methods, i.e., a first two-color print method by which a chromatic color is converted into red and an achromatic color is converted into black, and a second two-color print method by which a color having a hue similar to that of red is converted into red and a chromatic color having a hue different from that of red and an achromatic color are converted into black.
It is assumed that an original includes a document image in black characters, red characters, and other color characters written in a different color. Such an original is, for example, a document containing records of a meeting. In the document, an assignment to be done by the next meeting is written in red characters and a topic of the meeting is written in blue characters. Thus, the color characters, i.e., the red characters and the blue characters, can be more noticeable than the black characters thereby highlighting the assignment and the topic, and because the color characters are written in the two colors of red and blue, two different meanings can be indicated by the red characters and the blue characters. Because of improvement in colorization in recent years, a document created by using color characters in a plurality of colors is often used. If such a document is output in two colors by employing the first two-color print method, red characters and color characters written in a different color (the blue characters in the above example) are output in red, and black characters are output in black. Because both the red characters and the blue characters are output in red, it is difficult to recognize the characters originally written in red and the characters originally written in blue on an output image. Japanese Patent Application Laid-open No. H09-289592, Japanese Patent Application Laid-open No. H10-224608, and Japanese Patent Application Laid-open No. 2007-68127 propose technologies for solving the above problem. On the other hand, when the document is output in two colors by employing the second two-color print method, if the color of the color characters is not similar to red (for example, if the color characters are the blue characters), the red characters are output in red and the black characters and the color characters are output in black. Because both the black characters and the color characters are output in black, it is difficult to recognize the characters originally written in black and the characters originally written in the different color on an output image.
The color characters are used in the original because a specific area of a document needs to be highlighted. In the case of the first two-color print method, characters originally written in red are generally represented in darkest and brightest red (pure color) among color characters represented in red. As described in Japanese Patent Application Laid-open No. H10-224608, the red characters are represented in red with a thickly painted pattern. Thus, it is possible to maintain a highlighting effect generated by the red characters, whether it is intentional or not. On the other hand, in the case of the second two-color print method as disclosed in Japanese Patent Application Laid-open No. H09-289592, Japanese Patent Application Laid-open No. H10-224608, or Japanese Patent Application Laid-open No. 2007-68127, or a second two-color print method employed in a currently manufactured product, characters originally written in black are generally represented in darkest black, and it is difficult to maintain the highlighting effect generated by the blue characters. Although it has been considered sufficient to maintain the highlighting effect generated by at least the red characters upon a two-color output in black and red, the highlighting effect generated by the blue characters also needs to be maintained in view of the present situation where a document often includes color characters in a plurality of colors due to the improvement in the colorization. Although it is considered that, due to a request or a fixed concept of a user, the characters originally written in red and black need to be represented in red and black precisely as it is upon the two-color output in black and red, sometimes it is better to output the document in two colors such that the highlighting effect generated by the color characters can be maintained instead of representing the color characters precisely as it is. In the second two-color print method, according to Japanese Patent Application Laid-open No. H09-289592, Japanese Patent Application Laid-open No. H10-224608, and Japanese Patent Application Laid-open No. 2007-68127, although it is possible to represent the black characters such that the user can recognize the characters originally written in black and the characters originally written in a different color, it is difficult to maintain the highlighting effect generated by the characters originally written in the different color.